Osmolarity=osmole of the solute/litres of the solution ionic equation for dissociation of CaCl2 is CaCl2--->Ca2+ +2Cl- total osmoles for reaction are 1(Ca2+) + 2(Cl-)= 3 osmoles therefore
0.50 moles of CaCl2 x 3 osmoles/ 1mole of CaCl2 = 1.5osmoles osmolarity=1.5 /1.0 L=1.5 osmol/l